2GG 



THE CEPUALOPnORA. 



§ 229. 



uj^on itself; its posterior extremity soon assumes a spiral form and is 

 covered with an alveolate wrapper, upon which gradually appear the 

 convolutions of the shell, without there being formed, at the same time, 

 an operculum. During this period, the eyes, tentacles, border of the 

 mantle, and the foot, appear at the anterior extremity ; and, in the 

 interior, the auditive capsules, the intestinal canal, the liver and heart 

 are gradually developed. Here, therefore, the development of the 

 cephalic pinions, which characterize the embryos of the Branchiata, is also 

 incomplete. 



The development of the naked Pulmonata is quite different.'*' When 

 the round embryos begin to rotate, two crests appear side by side, upon 

 the previously divided vitellus ; one of these is changed into the shield and 

 into the respiratory and circulatory organs situated beneath, while the other 

 goes to form the foot. At its anterior extremity, appear the eyes, tenta- 

 cles, and lips; and at the posterior extremity, a peculiar contractile vesicle 

 is formed. This vesicle presses its contents towards the vitelline substance 

 which is still contained in a kind of vitelline sac projecting anteriorly 

 between the two crests, and which, also, becomes contractile. ''^^ By this 

 arrangement there is an interchange of the contents of the vitelline sac and 

 the caudal vesicle, due to their alternate contractions. Subsequently, the 

 liver and digestive canal are formed out of the vitelline substance between 

 the two crests. The vitelline sac and caudal vesicle are in this way con- 

 siderably diminished, and, at last, wholly disappear. 



The develojiment of Sagitta, as far as yet known, differs essentially from 

 that of the Gasteropoda,*"" in that its embryo is not formed at the expense 



Viri. 1837, p. 129, PI. III. IV ; Poticket, Aim. d. 

 Sc. Nat. X. 183S, p. 63 (Lymnaens) ; and Rathke, 

 Froriep's neue Not. XXIV. 1842, p. 161 {Lym- 

 naeus, Planorbis, ami Helix). 



C See Laurent, in the Ann. d. Sc. Nat. IV. 1835, 

 p. 248 {Limax and Arion); Van Heneden, and 

 Windischmann, in tlie Bull, de I'Acad. roy. de 

 Bnixelles, V. No. 5, p. 286, Ann. d. Sc. Nat. IX. 

 1838, p. 366, and in it/u//er's Arch. 1841, p. 176, 

 Taf. VII. VIII. (Limax).* 



7 This contractility shows itself quite early in the 



vitellus of the Limacina, for Dujardin (Ann. d. Sc. 

 Nat. VII.1S37, p. 374, or, Observ. au ilicrosc. Atlas, 

 1842, PI. V. tig. 10, 11) has seen in the eirgs of Li- 

 max cinereus soon after their deposition, singular 

 vitelline movements exactly resembling the alter- 

 nate protrusions and retractions of the parenchyma 

 of Amoeba. 



8 See the observations of Darwin, in the Ann, 

 of Nat. Hist. XIII. p. 4, or Ann. d. Sc. Nat. I. 

 1844, p. 363.t 



* [§229, note 6.] See also O. Schmidt (Ueber 

 die Entwickelung von Limax agrestis, in Miiller^s 

 Arch. 1851, p. 278) who differs in many points from 

 Fa« Beneden and Windischmann, as to the his- 

 tological development of some of the organs. See, 

 furthermore, Gesenbaur, Siebold and Ko//i/cer''s 

 Zeitsch. III. 1852, p. 371. — Ed. 



t [§ 229, note 8.] See, for some of the more re- 

 cent contributions to the embryology of the Ceplial- 

 ojjhora, Koren and Datiielssen (Bidrag til Pec- 

 tiui))ranchiernes Udvicklings histou-e, Bergen, 1851, 

 or its Translation into French in the Ann. d. Sc. 

 Nat. XVIII. 1852, p. 257, and XIX. 1853, p. 89), 

 and Gegenbatir (Beitriige zur Entwickelungsge- 

 schichte der Landgastropoden, in Siebold and Kiil- 

 liker^s Zeitsch. 111. 1852, p. 371.) These works are 

 quite complete as far as they go, and that of Ge- 

 genbaur, e.specially, has full details upon the form- 

 ation of all the organs and their mutual embryolog- 

 ical relations. No just resume can be given in the 

 proscribed limits of my notes. 



1 cannot here well omit at least an allusion to that 



most remarkable episode in the embryology of the 

 Mollusca, the development of certain MoUusks in 

 Holothurioidea. The facts of the case were discov- 

 ered and announced by J. Mailer (Veriiandl. der 

 Akad. zu Berlin, 1851, p. 628 (October 23), and 

 Nachtrag, p. 679 (Nov. 13), or in extenso in Mul- 

 ler''s Arch, 1852, p. 1), and they are indeed so 

 wonderful that it is well they were first brought out 

 by so reliable a physiologist and embryologist. 



The main facts, briefly sta,ted, are as follows : In 

 certain hidividuals of 5yna;)Za digitata there are 

 found from one to three sac-like bodies in the canty 

 of the body, and attached by their suiierior extremity 

 to the head, and I)y the lower end to the intestine ; 

 but this connection of the sac with the abdominal 

 and other organs, is one of simple contiguity and 

 not of very direct communication. The upper por- 

 tion of the sac is of a yellow, and the lower of a 

 green color ; the lower portion, moreover, ie intus- 

 susceptsd, with a bUnd end, like an inverted finger 

 of a glove. It is in this sac-like organ that are de- 

 veloped true Jlollusks ; in the upper or more ca- 



